How can I fix this "relpath" error
It looks like you are using relative paths but the files are in different drives and not in the folder where the project file is. Move all the files to a common directory, along with the project file, or disable relative paths, so that the files are in a fixed location.
From the blender manual:

Relative Paths
Many blend-files reference external images or other linked blend-files. A path tells Blender where to look for these files. If the external files are moved, the blend-file that references them will not look right.
When you specify one of these external files, the default option is to make the path relative. Blender stores a partial path evaluated relative to the directory location of the referencing blend-file. This choice helps when you need to reorganize folders or move your files.
With a relative path, you can move the blend-file to a new location provided the externally linked files are moved along with it. For example, you could send someone a folder that contains a blend-file and a sub-folder of external images that it references.
When relative paths are supported, the File Browser provides a Relative Path checkbox, when entering the path into a text field, use a double slash prefix (//) to make it so.